This research focuses on short and long-term changes that human mothers cause in their infants during nursing. In newborns it assesses how mothers protect against pain by combining orosensory (milk or sucrose) and tactile (pacifier sucking) aspects of the mother to determine the interactions between afferent systems during and following fluid infusion. Metabolic consequences of tasting sucrose of mile or sucking a pacifier will be evaluated via direct calorimetry. We have already demonstrated substantial reduction heat loss in infants tasting sucrose. Energy savings is common to the behavioral and physiological changes induced by sucrose and may serve as a basis for their selection. Opioid mechanisms underlying orosensory-induced changes will be assessed in infants with a prenatal methadone history. In principal, these infants, whose endogenous opioids have been reduced, should not respond to sweet taste but should be calmed by a pacifier. The role of nonnutritive sucking in conserving energy in those infants will be determined. We will also determine the stable and changing proximal maternal stimuli that calm distressed 6 to 12-week olds and serve as a basis for maternal preference. We have shown that orosenory stimulation claims at 2-weeks; it must be combined with visual engagement to calm 4-9 week olds. This combination does not calm at 12 weeks. The need for eye engagement to calm 4-9-week-old infants leads us to investigate whether these infants use internal facial features to recognize familiar adults or to continue to rely on external features as do newborns. This is an important issue from the perspective of what defines familiarity and safety, the experiences necessary to cause these changes and the underlying neurology. This research will reveal behavioral, metabolic, and physiological consequences of nursing-suckling interactions during the first three postnatal months. It will impact on patient treatment from the perspective of pain management and recovery from remarkable prenatal histories. It makes significant empirical contributions to what infants can and do learn during nursing and its biological significance.